U.S. patent application number 11/321463 was filed with the patent office on 2006-07-27 for method of manufacturing dispersible colorant and ink-jet recording ink.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Makoto Aoki, Yoko Ichinose, Toshiaki Kaneko, Masashi Miyagawa, Yoshio Nakajima, Junichi Sakai.
Application Number | 20060167136 11/321463 |
Document ID | / |
Family ID | 35781941 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060167136 |
Kind Code |
A1 |
Kaneko; Toshiaki ; et
al. |
July 27, 2006 |
Method of manufacturing dispersible colorant and ink-jet recording
ink
Abstract
A dispersible colorant suitable for ink-jet recording ink is
manufactured by a method using aqueous precipitation
polymerization. The ink has high dispersion stability and can form
a high-quality image excellent in fastness properties. The method
includes at least a dispersing step of dispersing a colorant into
an aqueous solution by means of a dispersant, an aqueous
precipitation polymerization step of adding a resin monomer and a
radical polymerization initiator to the solution into which the
colorant is dispersed to manufacture a dispersible colorant having
a chargeable resin pseudo-fine particle, fixing thereon by means of
aqueous precipitation polymerization, and an ultrafiltration step
of subjecting the aqueous solution containing the dispersible
colorant to ultrafiltration to obtain the dispersible colorant.
Inventors: |
Kaneko; Toshiaki; (Tokyo,
JP) ; Miyagawa; Masashi; (Yokohama-shi, JP) ;
Aoki; Makoto; (Yokohama-shi, JP) ; Sakai;
Junichi; (Tokyo, JP) ; Nakajima; Yoshio;
(Yokohama-shi, JP) ; Ichinose; Yoko; (Tokyo,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
35781941 |
Appl. No.: |
11/321463 |
Filed: |
December 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP05/12294 |
Jun 28, 2005 |
|
|
|
11321463 |
Dec 30, 2005 |
|
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Current U.S.
Class: |
523/160 ;
523/161; 524/800 |
Current CPC
Class: |
C09D 11/326
20130101 |
Class at
Publication: |
523/160 ;
523/161; 524/800 |
International
Class: |
C03C 17/00 20060101
C03C017/00; C09D 11/00 20060101 C09D011/00; C08G 73/02 20060101
C08G073/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2004 |
JP |
2004-190472 (PAT. |
Claims
1. A method of manufacturing a dispersible colorant using aqueous
precipitation polymerization, comprising at least: a dispersing
step of dispersing a colorant into an aqueous solution by means of
a dispersant; an aqueous precipitation polymerization step of
adding a resin monomer and a radical polymerization initiator to
the solution into which the colorant is dispersed to manufacture a
dispersible colorant having a chargeable resin pseudo-fine particle
fixing on the colorant by means of aqueous precipitation
polymerization; and an ultrafiltration step of subjecting the
aqueous solution containing the dispersible colorant to
ultrafiltration to obtain the dispersible colorant.
2. A method of manufacturing a dispersible colorant according to
claim 1, wherein the resin obtained by the aqueous precipitation
polymerization has a weight average molecular weight of 2,000 or
more and 20,000 or less.
3. A method of manufacturing a dispersible colorant according to
claim 1, wherein the aqueous precipitation polymerization step is
performed through two stages composed of: a first stage involving
adding one or more kinds of hydrophobic monomers and one or more
kinds of hydrophilic monomers for aqueous precipitation
polymerization by means of a water-soluble radical polymerization
initiator; and a second stage involving further adding one or more
kinds of hydrophilic monomers for aqueous precipitation
polymerization by means of a water-soluble radical polymerization
initiator after the first stage.
4. A method of manufacturing a dispersible colorant according to
claim 1, wherein the content of a resin not fixing on the colorant
in a 10-mass % aqueous solution of the dispersible colorant
obtained after the ultrafiltration step is 0.1 mass % or less.
5. A method of manufacturing a dispersible colorant according to
claim 1, wherein the ultrafiltration step comprises: adjusting the
pH of the aqueous solution containing the dispersible colorant
obtained by the aqueous precipitation polymerization step to be 9
or more and 13 or less; and adding a water-soluble organic solvent
for ultrafiltration.
6. A method of manufacturing a dispersible colorant according to
claim 5, wherein the amount of the water-soluble organic solvent to
be added is 5 mass % or more and 40 mass % or less with respect to
the aqueous solution containing the dispersible colorant.
7. A method of manufacturing a dispersible colorant according to
claim 5, wherein the water soluble organic solvent comprises a
polyhydric alcohol.
8. A method of manufacturing a dispersible colorant according to
claim 7, wherein the polyhydric alcohol comprises diethylene
glycol.
9. A method of manufacturing a dispersible colorant according to
claim 1, wherein a chain transfer agent is used as a molecular
weight adjustor in the aqueous precipitation polymerization
step.
10. A method of manufacturing a dispersible colorant according to
claim 9, wherein the chain transfer agent comprises a compound
having a thiol group.
11. A method of manufacturing a dispersible colorant according to
claim 10, wherein the compound having a thiol group comprises one
selected from the group consisting of lauryl mercaptan, octyl
mercaptan, 2-mercaptoethanol, octyl thioglycolate, and
3-mercaptopropionic acid.
12. An ink-jet recording ink comprising a dispersible colorant
obtained by means of the method of manufacturing a dispersible
colorant according to claim 1.
Description
[0001] This application is a continuation of International
Application No., PCT/JP2005/012294, filed on Jun. 28, 2005, which
claims the benefit of Japanese Patent Application No. 2004-190472
filed on Jun. 28, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of manufacturing a
dispersible colorantcolorant; and an ink-jet recording ink
containing a dispersible colorantcolorant obtained by means of thee
method.
[0004] 2. Related Background Art
[0005] An ink-jet system is a process for recording an image,
characters, or the like by making minute liquid droplets of ink to
fly out of nozzles onto a recording medium (e.q., paper) with any
of various operating principles, and facilitates high speed,
low-noise, and multicolor recording. Besides, the ink jet system is
characterized in higher versatility of recording patterns and no
manipulation for development and fixation, and has rapidly become
popular in various applications. In recent years, particularly,
technologies for a full color ink-jet recording system with aqueous
ink have been remarkably developed, allowing the formation of a
color image without inferiority in comparison to any multicolor
recording by the conventional plate-making system or any copy
formed by the conventional color photographic system. When the
number of copies to be printed is small, the ink-jet recording
system attains printed articles more cheaply than those obtained by
the conventional multicolor printing or copy. Therefore, the
ink-jet recording system becomes widespread in the field of full
color image-recording.
[0006] Furthermore, in association with improvements of recording
properties such as high speed, high definition, and full-color, an
ink-jet recording apparatus and an ink-jet recording method have
been improved. In general, for example, ink-jet recording ink for
use in an ink-jet recording apparatus is requested to: (1) provide
a high-resolution, high-density, and uniform image causing neither
feathering nor fog on paper; (2) provide good ejection
responsiveness and good ejection stability at all times without
causing clogging due to the drying of ink at the tip of a nozzle;
(3) provide good fixability of ink on paper; (4) provide a formed
image with good fastness properties (such as rub-off resistance);
and (5) provide good long-term storage stability. In particular, in
association with a recent increase in printing speed, ink which can
be dried and fixed quickly and which allows an image with high
quality to be recorded has been requested.
[0007] ColorantColorants used in the ink-jet recording system
mainly include dyes and pigments. In terms of manageability and
high coloring property for aqueous ink, conventionally, a
water-soluble dye has been mainly used. However, in late years, the
development of ink using, as a colorantcolorant for aqueous ink
capable of realizing higher weatherability of an image, an
essentially water-insoluble colorantcolorant, particularly pigment
has been advanced. For the use of a water-insoluble
colorantcolorant, particularly a pigment as aqueous ink, there is a
need of stably dispersing the colorantcolorant into water. In this
case, conventionally, the process for attaining stability in
dispersion typically using a surfactant or a polymer-dispersant
(also referred to as a dispersion resin) has been employed.
[0008] Alternatively, there is proposed a procedure for chemically
modifying the surface of a water-insoluble colorantcolorant to make
the water-insoluble colorantcolorant self dispersible (see, for
example, JP 10-195360 A). On the other hand, microcapsule type
pigments that are covered with resin have been proposed (see, for
example, JP 08-183920 A and JP 2003-34770 A) In JP 2003-34770 A,
there is disclosed "an aqueous dispersion of colored fine
particles, characterized by comprising a water-insoluble coloring
agent, where the water-insoluble coloring agent was dispersed into
an aqueous medium in the presence of a dispersant and then added
with a vinyl monomer to initiate polymerization, wherein the
dispersion shows dispersion stability when the dispersant has
dispersed the water-insoluble coloring agent, while the latex
caused has poor dispersion stability when the vinyl monomer was
polymerized in the presence of only the dispersant". "When the
emulsion polymerization of a vinyl monomer with a dispersion of
water-insoluble coloring agent occurs, the dispersant is hardly
detached from the surface of pigments and the polymerization occurs
on the surface of pigments adsorbing the dispersant because of
insufficient affinity of the dispersant to the vinyl monomer or the
obtained polymer". Therefore, "a dispersion of fine particles or
pigments the surface of which is covered, can be obtained in high
yield without causing aggregation". The use of the dispersion of
colored fine particles results in aqueous ink having excellent
dispersion stability and print adequacy with no paper-type
dependency and little metallic luster, while being excellent in
water resistance, light resistance, and rub-off resistance.
SUMMARY OF THE INVENTION
[0009] However, the technology described above may be insufficient
in dispersion stability of a colorantcolorant and gloss of a
recorded image. According to the study of the inventors of the
present invention, the surface functional group density on a
colorantcolorant should be raised in order to enhance dispersion
stability. However, in the conventional procedure using a polymer
dispersant or the procedure, in which pigments are covered with a
resin, proposed in JP 08-183920 A, long-term storage stability may
be hardly sustained as the resin tends to be detached from the
colorantcolorant with time because of an increase in hydrophilicity
of the resin, in proportion to an increase in acid value of the
resin to enhance dispersion stability. On the other hand, in an
approach to chemically modifying the surface of a water-insoluble
colorantcolorant by means of a method disclosed in JP 10-195360 A,
the kinds and density of functional groups with which the surface
can be modified are limited. In addition, direct chemical
modification of a colorantcolorant, especially an organic pigment,
involves the occurrence of so-called "pigment-detachment" in which
a pigment molecule which is intrinsically insoluble in water to be
crystallized is solubilized by bonding with a hydrophilic group to
be eluted from a pigment particle. As a result, a color tone
significantly changes (see FIGS. 6A and 6B). Therefore, the
approach is not at a sufficiently satisfactory technical level.
[0010] An object of the present invention is to provide a method of
manufacturing a dispersible colorantcolorant which: has solved
those conventional problems; has sufficiently high dispersion
stability; is not detached from a resin component; can form a
high-quality image excellent in fastness properties; hardly
contaminates a face surface of a head when it is used for ink-jet
recording ink; hardly causes kogation on a heater board; and can
provide excellent ejection stability, and to provide an ink-jet
recording ink containing the dispersible colorantcolorant.
[0011] The inventors of the present invention have made extensive
studies about means for achieving the above object. As a result,
they have achieved the development of a method of manufacturing a
novel dispersible colorantcolorant which: maintains high dispersion
stability; is not detached from a resin component; and is excellent
in storage stability for a long time period, the dispersible
colorantcolorant having a novel shape. The inventors have used such
dispersible colorantcolorant to manufacture ink-jet recording ink
which: has ejection stability and dispersion stability sufficient
for ink-jet recording applications; can form a high-quality image
excellent in fastness properties such as rub-off resistance; hardly
contaminates a face surface of a head; and hardly causes kogation
on a heater board.
[0012] That is, according to one aspect of the present invention,
there is provided a method of manufacturing a dispersible
colorantcolorant using aqueous precipitation polymerization
including at least: a dispersing step of dispersing a
colorantcolorant into an aqueous solution by means of a dispersant;
an aqueous precipitation polymerization step of adding a resin
monomer and a radical polymerization initiator to the solution into
which the colorantcolorant is dispersed to manufacture a
dispersible colorantcolorant having a chargeable resin pseudo-fine
particle fixing on the colorantcolorant by means of aqueous
precipitation polymerization; and an ultrafiltration step of
subjecting the aqueous solution containing the dispersible
colorantcolorant to ultrafiltration to manufacture a dispersible
colorantcolorant
[0013] According to another aspect of the present invention, there
is provided an ink-jet recording ink containing a dispersible
colorantcolorant obtained by means of the above manufacturing
method.
[0014] According to the present invention, a dispersible
colorantcolorant on which a chargeable resin pseudo-fine particle
fixes suitable for ink-jet recording ink can be selectively
obtained with high degree of purity through an extremely simple
aqueous precipitation polymerization step not involving the use of
a water-insoluble solvent by placing an ultrafiltration
purification step after the aqueous precipitation polymerization
step. Ink containing a dispersible colorant on which a chargeable
resin pseudo-fine particle fixes obtained by means of the
manufacturing method is very excellent in ejection stability while
it has the colorant dispersed by a resin.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIGS. 1A and 1B are schematic views for illustrating the
basic structure of a dispersible colorant obtained by the present
invention on (to) which chargeable resin pseudo-fine particles fix
(fuse);
[0016] FIGS. 2A, 2B, 2C, and 2D are schematic views of typical
steps of the manufacturing method of the present invention,
respectively;
[0017] FIG. 3 is a schematic view for illustrating the steps of
producing chargeable resin pseudo-fine particles and allowing the
particles to fix (fuse) on (to) a colorant in the manufacturing
method of the present invention;
[0018] FIG. 4 is an enlarged schematic view of chargeable resin
pseudo-fine particles obtained by the present invention viewed from
an interface on which the particles fix (fuse) on (to) the
colorant;
[0019] FIG. 5 is an enlarged schematic view of the interface on
which the chargeable resin pseudo-fine particles obtained by the
present invention fix (fuse) on (to) the colorant; and
[0020] FIGS. 6A and 6B are schematic views of a pigment-detachment
phenomenon occurred at the time of direct modification with a
hydrophilic group on an organic pigment, represented by JP
10-195360 A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Hereinafter, the present invention will be described in more
detail by way of a preferred embodiment.
[0022] A first feature of a dispersible colorant manufactured by
the present invention lies in that the dispersible colorant
includes a colorant and a chargeable resin pseudo-fine particle,
and the colorant has the chargeable resin pseudo-fine particle
fixing thereon. FIGS. 1A and 1B are schematic views each showing a
dispersible colorant having a colorant 1 on which chargeable resin
pseudo-fine particles 2 fix, which characterizes the present
invention. The part 2' shown in FIG. 1B is a part schematically
showing a state in which part of the chargeable resin pseudo-fine
particles 2 fixing on the surface of the colorant 1 fuse.
[0023] A chargeable resin pseudo-fine particle fixes on a colorant,
whereby charge is imparted by the chargeable resin pseudo-fine
particle to the surface of the colorant. As a result, the colorant
becomes a dispersible colorant that can be dispersed into water or
an aqueous ink medium. At the same time, the dispersible colorant
has excellent adhesiveness to a recording medium because it has a
resin component fixing on its surface. At this time, the chargeable
resin pseudo-fine particle does not adhere to the colorant owing to
mere physical adsorption of the resin component, but fixes on the
colorant, which is characteristic of the dispersible colorant to be
used in the present invention. As a result, the chargeable resin
pseudo-fine particle is not detached from the surface of the
colorant. Therefore, the dispersible colorant to be used in the
present invention is excellent in long-term storage stability as
well.
[0024] Here, the term "chargeable resin pseudo-fine particle" as
used herein refers to a resin aggregate in a state where resin
components are strongly aggregated. Preferably, in the resin
aggregate, many physical cross-linkages are formed (the resin
aggregate is resin components having a stable configuration as a
fine particulate configuration or a minute aggregate close to the
fine particle configuration). The details of the chargeable resin
pseudo-fine particles will be described later.
[0025] The state in which the chargeable resin pseudo-fine particle
fixes on the colorant in the present invention depends on a strong
interaction between the surface of the colorant and the chargeable
resin pseudo-fine particle. The state may be expected as the
following. FIG. 4 shows an enlarged schematic view of the
interface, between the chargeable resin pseudo-fine particle and
the colorant. First of all, the chargeable resin pseudo-fine
particle 2 is formed by intertwined polymers composed of various
monomer unit compositions (represented by 9-1 and 9-2 in the
figure). On the interface with the colorant, the polymers locally
take various structures and hence cause variations in their local
surface energy states, respectively. At a point (part shown by a
black circle in the figure) where the surface energy caused from
the chemical and surface structures of the colorant and the surface
energy caused from the chemical and surface structures of the
polymer are locally well coincident with each other, the colorant
and the polymer are tightly bound together. Furthermore, on the
interface where one of the chargeable resin pseudo-fine particles
interfaces on the colorant, as shown in FIG. 4, there are multiple
points such as those represented by 10, where the surface energies
of both the colorant and the polymer are locally coincident. It is
expected that a strong interaction among the multiple points
results in the fixing state of the present invention. In the
present invention, such as one represented by 2' in FIG. 1B, the
state in which part of the surface area (e.g., 30% or more thereof)
of the chargeable pseudo-fine particle is in touch with the
colorant is referred to as "fusion" for convenience. However, it is
one of the forms of fixing, so the chargeable pseudo-fine particle
and the colorant may not be blended in each other in their
interface.
[0026] In particular, strong interactions are exerted among
constituent polymers inside the chargeable resin pseudo-fine
particle, so, in some cases, the constituent polymers are twisted
up each other and physical linkages are formed among them. Thus,
even in the case where the chargeable resin pseudo-fine particle
has many hydrophilic groups, no chargeable resin pseudo-fine
particle fixing on the colorant is detached therefrom, or no resin
components having hydrophilic groups is continuously eluted out of
the chargeable resin pseudo-fine particle. In contrast, such
encapsulation method as disclosed in JP 08-183920 A may not provide
sufficient long-term storage stability because a resin having high
hydrophilicity cannot strongly bind to a colorant, so it is
detached from the colorant.
[0027] In addition, as a merit of allowing the chargeable resin
pseudo-fine particle to fix on the colorant in the dispersible
colorant to be used in the present invention, such a configuration
increases the specific surface area of the dispersible colorant
and, on many portions of the surface of the colorant, charge on the
surface of the chargeable resin pseudo-fine particle can be
distributed. As a result, the dispersible colorant has a high
specific surface area, so the charge of the chargeable resin
pseudo-fine particles can be provided as charge on the surface of
the dispersible colorant with extremely high efficiency. In other
words, the configuration of the dispersible colorant to be used in
the present invention is a configuration that more efficiently
provides the surface of the dispersible colorant with more surface
charge. Therefore, the above configuration of the dispersible
colorant of the present invention can provide higher dispersion
stability than that of the configuration of a colorant covered with
a resin as typified by JP 08-183920 A even when a resin component
has a smaller substantial acid value or amine value.
[0028] In general, an organic pigment is insolubilized (turned into
a pigment) by the crystallization of a colorant molecule having
coloring property due to a strong interaction. In the case of a
dispersible colorant using an organic pigment as the colorant to be
used in the present invention, as described above, multiple
interaction points are randomly distributed at the interface
between the chargeable resin pseudo-fine particle and the colorant.
Thus, the chargeable resin pseudo-fine particles 11 can fix over
several colorant molecules 1a in the pigment particles (see FIG.
5). Therefore, the "pigment detachment", which occurs when the
colorant molecule 1a is locally provided with hydrophilicity by a
hydrophilic group 12, as explained by FIGS. 6A and 6B, does not
occur in the present invention. Preferably, when the organic
pigment is used as a colorant, the size of the chargeable resin
pseudo-fine particle may be adjusted so as to be smaller than the
particle size of the dispersed pigment but larger than the colorant
molecule. Consequently, a dispersible colorant using an organic
pigment provided with high dispersibility can be obtained without
any disturbance of the crystal structure of the pigment.
[0029] In the present invention, the state where the colorant
"fixes" the chargeable resin pseudo-fine particles can be confirmed
by the procedure with three separation stages for facility as
described below. At first, the first separation separates the
colorant to be confirmed from other water-soluble components
(including a water-soluble resin component) in ink or a water
dispersing element. Then, the second separation separates the
colorant in a sediment generated by the first separation from a
water-insoluble resin component. Furthermore, the third separation
separates the resin component being absorbed weakly from the
dispersible colorant fixing chargeable resin pseudo-fine particles.
Subsequently, the quantitative determination of the resin component
in the supernatant obtained by the third separation and comparison
between the sediment from the second separation and the sediment
from the third separation are carried out, respectively.
Consequently, the fixation between the colorant and the chargeable
resin pseudo-fine particle can be confirmed.
[0030] More specifically, for example, the fixation can be
confirmed by the following conditions. 20 g of ink or a water
dispersing element into which a colorant is dispersed are taken and
then adjusted so that the mass of the total solid content can be
about 10%, followed by the first separation by means of a
centrifugal separator at 12,000 rpm for 60 minutes. Among the
separated products, the sediment of the lower layer containing the
colorant is re-dispersed in about three volumes of pure water and
then the whole is subjected to the second separation at 80,000 rpm
for 90 minutes. The sediment of the lower layer containing the
colorant re-dispersed in three volumes of pure water is subjected
to the third separation at 80,000 rpm for 90 minutes, to thereby
take out the sediment of the lower layer containing the colorant.
Each of the sediments from the second and third separations is
taken so as to be about 0.5 g in solid content, followed by drying
at 30.degree. C. for 18 hours under reduced pressures. The
resulting product is observed by a scanning electron microscope at
a magnification of 50,000. It is determined that resin pseudo-fine
particles fix on the colorant when the multiple fine particulate
substances or minute aggregates based thereon, which are attached
on the surface of the observed dispersible colorant, were confirmed
and when the sediments from the second and third separation have
the same configuration. Furthermore, the supernatant fraction of
the upper layer obtained by the third separation is gently taken so
as to become almost half in volume and the percent mass of a solid
content is then calculated from variations in mass before or after
drying at 60.degree. C. for 8 hours. When the variations are less
than 1%, the resin pseudo-fine particles may not be detached from
the dispersible colorant. Thus, it can be judged that the resin
pseudo-fine particles have fixed on the dispersible colorant.
[0031] The conditions of the respective separations described above
are preferable examples. Any of other separation methods or
separation conditions may be applied as a method of determining the
dispersible colorant to be used in the present invention as far as
it is a procedure for attaining the intents of the first, second,
and third separation procedures. In other words, the first
separation intends to separate the colorant in ink and a water
dispersing element and the resin component adsorbed thereon from
the water soluble component. The second separation intends to
separate the colorant and the resin component fixing on the
colorant from other resin components adsorbed on the colorant.
Furthermore, the third separation intends to confirm that the resin
component fixing on the colorant is not detached therefrom.
Needless to say, any of other known or newly developed separation
procedures may be used as far as it is a separation procedure for
attaining the respective intents of the first, second, and third
separation procedures. Besides, the number of the separation
procedures to be applied may be smaller or larger than three.
[0032] A second feature of the dispersible colorant to be used in
the present invention lies in that the dispersible colorant can be
independently dispersed into an aqueous medium while allowing the
chargeable resin pseudo-fine particle 2 to fix on the
water-insoluble colorant 1. As described above, the dispersible
colorant to be used in the present invention is a self-dispersible
colorant, which can be essentially dispersed into water or aqueous
ink in a stable manner even without the aid of another substance
such as a surfactant or a polymer dispersant. The definition and
criterion of such a term will be described later in detail.
Therefore, the dispersible colorant to be used in the present
invention does not require the addition of a polymer dispersant or
any other resin component, which may be detached in the long term,
or of a surfactant component, for the purpose of stabilizing the
dispersion of the colorant. As a result, when the dispersible
colorant to be used in the present invention is used as the aqueous
ink, the design freedom with respect to any component except the
dispersible colorant becomes large. For instance, aqueous ink can
be prepared as one which is capable of attaining a sufficiently
high printing density even on a recording medium having high
permeability to ink, such as plain paper.
[0033] The self-dispersibility of the dispersible colorant to be
used in the present invention can be confirmed, for example, by the
following method. The ink or water dispersing element into which
the colorant is being dispersed is diluted with pure water by
10-fold and then condensed up to the original concentration using
an ultrafilter with a molecular weight cut off of 50,000.
Subsequently, the concentrate is separated by a centrifugal
separator at 12,000 rpm for 2 hours, and a sediment is then
collected and re-dispersed into pure water. At this time, the
sediment which can be re-dispersed well is defined as one having
self-dispersibility. It is collectively determined whether or not
the sediment is re-dispersed well by the criteria, for example, as
follows: the uniform dispersion is observed by sight; any
conspicuous sediment occurs while standing for 1 to 2 hours; even
if the sediment has occurred, it can be restored by shaking; when
the diameters of the dispersed particles are measured by means of
dynamic light scattering, the average particle size of the
dispersed particles is within the range of 2 folds of the particle
size before the operation.
[0034] As described above, the dispersible colorant to be used in
the present invention has the form having a high specific surface
area as the colorant fixes the chargeable resin pseudo-fine
particle. The dispersible colorant has much charge on its wide
surface, so it realizes excellent storage stability. Therefore, the
chargeable resin pseudo-fine particles provide further preferable
results when many (multiple) chargeable resin pseudo-fine particles
are dotted and fix on the colorant. In particular, it is desirable
that there be a predetermined distance between the fixing
chargeable resin pseudo-fine particles, preferably with uniform
distribution for the colorant, more preferably in the state that
part of the surface of the colorant particle is exposed between the
chargeable resin pseudo-fine particles. Such conditions can be
confirmed by observing the aqueous ink according to the present
invention with a transmission electron microscope or a scanning
electron microscope. In other words, the multiple chargeable resin
pseudo-fine particles are observed to fix on the surface of the
colorant while keeping a predetermined distance between the
particles, or the surface of the colorant is observed to be exposed
between the chargeable resin pseudo-fine particles fixing thereon.
Furthermore, the chargeable resin pseudo-fine particles may be
observed such that they are partially in close proximity to one
another or fused together. However, in any of those cases, there is
a certain distance between the chargeable resin pseudo-fine
particles as a whole and there are some exposed portions of the
surface of the colorant. Besides, when such states are distributed,
it will be evident for a person skilled in the art that the
chargeable resin pseudo-fine particles are deemed to be dotted and
fix on the colorant.
[0035] Furthermore, it has become evident that the aqueous ink
containing the dispersible colorant to be used in the present
invention having such characteristics as described above shows
excellent quick-drying property on a recording medium. This reason
is not sure, but it may depend on the following mechanism. As
described above, the dispersible colorant is dispersed into ink in
the state that the chargeable resin pseudo-fine particles fix on
the surface of the colorant. When the ink reaches a recording
medium, the aqueous solvent in the ink (hereinafter, referred to as
an ink solvent) is absorbed into fine pores on the recording medium
(gaps between cellulose fibers in the case of plain paper, while
fine pores in a receiving layer of coated or glossy paper) through
a capillary phenomenon. Then, on the dispersible colorant to be
used in the present invention, owing to the structural features of
the material, there are chargeable resin pseudo-fine particles
dotted on the portion where the colorants contact with each other,
thereby forming many fine gaps. As a result, a capillary phenomenon
acts on the ink solvent existing between colorants, so the ink
solvent between the colorants can be quickly absorbed in the
recording medium. Out of the aqueous inks according to the present
invention, one using a dispersible colorant configured such that
chargeable resin pseudo-fine particles are dotted on its surface
shows more preferable quick-drying property. Therefore, it is
expected that the quick-drying property can be achieved by the
mechanism described above.
[0036] The surface functional group density of the dispersible
colorant according to the present invention is preferably.250
.mu.mol/g or more and less than 1,000 .mu.mol/g, or more preferably
290 .mu.mol/g or more and less than 900 .mu.mol/g. A dispersible
colorant having a surface functional group density smaller than the
above range may be poor in long-term storage stability. In
addition, a dispersible colorant having a surface functional group
density considerably larger than the above range has excessively
high dispersion stability, so it is apt to penetrate into a
recording medium, and hence it may be difficult to ensure a high
printing density.
[0037] The surface functional group density is determined, for
example, as follows. First, a large excessive amount of an aqueous
solution of hydrochloric acid (HCl) is added to a water dispersing
element or ink containing a dispersible colorant to be measured,
and the whole is centrifuged at 20,000 rpm for 1 hour by means of a
centrifugal separator for precipitation. The precipitate is
recovered and re-dispersed into pure water, and a solid fraction is
determined by means of a drying process. The re-dispersed
precipitate is weighed. A known amount of sodium hydrogen carbonate
is added, and the whole is stirred to prepare a dispersion liquid.
The dispersion liquid is additionally centrifuged at 80,000 rpm for
2 hours by means of a centrifugal separator for precipitation. The
supernatant is weighed, and a neutralization amount is determined
from neutralization titration by means of 0.1N hydrochloric acid.
The known amount of sodium hydrogen carbonate is subtracted from
the neutralization amount to determine the surface functional group
density as a number of moles per 1 g of the colorant.
[0038] Next, the respective components constituting the dispersible
colorant to be used in the present invention will be described.
[Colorant]
[0039] A colorant, which is one of the components of the
dispersible colorant to be used in the present invention, will be
described. Out of the conventionally known colorants and the
colorants to be newly developed, a colorant which is insoluble in
water and can be stably dispersed into water together with a
dispersant is desirably used as the colorant to be used in the
present invention. Examples of such colorant include a hydrophobic
dye, an inorganic pigment, an organic pigment, a metal colloid, and
a colored resin fine particle. A colorant having a particle size of
a dispersed particle in the range of preferably 0.01 to 0.5 .mu.m
(10 to 500nm), or particularly preferably 0.03 to 0.3 .mu.m (30 to
300 nm) is used. The dispersible colorant using a colorant
dispersed to have a particle size in such range becomes a
preferable dispersible colorant which provides an image having high
coloring power and high weatherability when the dispersible
colorant is used as aqueous ink. Such particle size of a dispersed
particle is a cumulant average value of particle sizes measured by
means of dynamic light scattering.
[0040] Examples of the inorganic pigment that may be usefully used
for a colorant in the present invention include carbon black,
titanium oxide, zinc white, zinc oxide, tripon, iron oxide, cadmium
red, molybdenum red, chromium vermilion, molybdate orange, chromium
yellow, chromium yellow, cadmium yellow, yellow oxide, titanium
yellow, chromium oxide, viridian, cobalt green, titanium cobalt
green, cobalt chromium green, ultramarine, ultramarine blue, iron
blue, cobalt blue, cerulean blue, manganese violet, cobalt violet,
and mica.
[0041] Examples of the organic pigment that may be usefully used in
the present invention include various pigments such as azo-based,
azomethine-based, polyazo-based, phthalocyanine-based,
quinactidone-based, anthraquinone-based, indigo-based,
thioindigo-based, quinophthalon-based, benzimidazolon-based,
isoindoline-based and isoindolinon-based pigments.
[0042] Examples of an organic water-insoluble color material that
may be used in the present invention include hydrophobic dyes such
as azo-based, anthraquinone-based, indigo-based,
phthalocyanine-based, carbonyl-based, quinonimine-based,
methine-based, quinoline-based, and nitro-based dyes. Of those, a
disperse dye is particularly preferable.
[0043] [Chargeable Resin Pseudo-Fine Particles]
[0044] The chargeable resin pseudo-fine particles, which are other
components of the dispersible colorant to be used in the present
invention, are defined as a microbody obtained by the agglomeration
of resin components each of which: is substantially insoluble in
water; has a small dispersion unit (particle size of a dispersed
particle) in water (or ink) of a colorant on which the components
are to fix; and has a sufficiently high degree of polymerization.
The microbody is virtually close to a spherical body, or the sizes
of multiple microbodies (the chargeable resin pseudo-fine
particles) match with each other in a certain range. The resin
components constituting the chargeable resin pseudo-fine particles
are desirably physically or chemically cross-linked with each
other. Whether the resin components constituting the chargeable
resin pseudo-fine particles are cross-linked with each other can be
confirmed by means of, for example, the following approach. The
resin components constituting the chargeable resin pseudo-fine
particles are estimated in advance by means of a conventional
analysis method. Linear polymers having the same chemical
structure, (or the same monomer unit composition) are synthesized
by means of solution polymerization, and the chargeable resin
pseudo-fine particles and the polymers are each impregnated with an
organic solvent as a good solvent to the polymers to compare the
solubilities of the particles and polymers. When the solubility of
each of the chargeable resin pseudo-fine particles is lower than
that of each of the polymers, the chargeable resin pseudo-fine
particles are cross-linked inside them.
[0045] As another preferable embodiment, the cumulant average value
of the particle sizes of the chargeable resin pseudo-fine particles
dispersed into water, if measurable by means of dynamic light
scattering, is desirably in the range of 10 nm or more, to 200 nm
or less. The polydispersity index of the particle sizes of the
dispersed particles is preferably less than 0.2 from the viewpoint
of long-term storage stability of the dispersible colorant. When
the center value of the particle sizes of the dispersed particles
is larger than 200 nm or the polydispersity index is larger than
0.2, an original object, that is, to finely disperse, and stabilize
the dispersion of the colorant, cannot be sufficiently achieved in
some cases. When the average value of the particle sizes of the
dispersed particles is smaller than 10. nm, the forms as the
chargeable resin pseudo-fine particles cannot be maintained
sufficiently, and the resin is apt to be dissolved into water, so
no merit of the present invention is obtained in some cases. On the
other hand, the stabilization of dispersion of the colorant by the
fixing of the chargeable resin pseudo-fine particles in the present
invention is effectively expressed when the average value is in the
range of 10 nm or more to 200 nm or less and the diameters of the
chargeable resin pseudo-fine particles are smaller than those of
the colorant particles themselves. The above preferable embodiment
holds true for the case where the particle sizes of the dispersed
chargeable resin pseudo-fine particles cannot be measured, and in
such case, the average particle size of the chargeable resin
pseudo-fine particles determined as a result of observation with an
electron microscope may be in the preferable range described above
or a range comparable thereto.
[0046] In addition, when the colorant is an organic pigment, on
condition that the above range is satisfied, the size of each of
the chargeable resin pseudo-fine particles is particularly
desirably smaller than the particle size of the dispersed pigment
and larger than the size of the colorant molecule as described
above because a dispersible colorant having an extremely stable
structure and high dispersibility can be obtained.
[0047] The term "chargeable" as used herein refers to a state where
a chargeable one holds a certain form of ionized functional group
in an aqueous medium, or desirably is self-dispersible because of
its chargeability. Accordingly, whether the particles are
chargeable resin pseudo-fine particles can be confirmed by a method
involving measuring the surface zeta potential of each of the
chargeable resin pseudo-fine particles by any one of conventionally
known and arbitrary approaches, a method involving: performing
potentiometric titration by means of an approach to be described
later; and calculating the chargeability as a functional group
density, a method involving adding an electrolyte to the water
dispersing element of the chargeable resin pseudo-fine particles to
confirm the dependence of the dispersion stability on the
electrolyte concentration, or a method involving performing
chemical structural analysis of the chargeable resin pseudo-fine
particles by means of a conventional approach to examine the
presence or absence of an ionic functional group.
[0048] Any resin components composed of, for example, natural or
synthetic polymers to be generally used and polymers to be newly
developed for the present invention can be used as the resin
components constituting the chargeable resin pseudo-fine particles
without any limitation. Examples of an available resin component
include an acrylic resin, a styrene/acrylic resin, a polyester
resin, a polyurethane resin, a polyurea resin, a polysaccharide,
and a polypeptide. In particular, a polymer or copolymer of a
monomer component having a radical polymerizable unsaturated bond
to which an acrylic resin or a styrene/acrylic resin belongs can be
preferably used because it can be generally used and simplifies the
functional design of the chargeable resin pseudo-fine
particles.
[0049] Specific examples thereof include: monomers each having a
carboxyl group such as acrylic acid, methacrylic acid, ecrotonic
acid, ethacrylic acid, propyl acrylic acid, isopropyl acrylic acid,
itaconic acid, and fumaric acid, and salts of them; monomers each
having a sulfonic group such as styrenesulfonic acid, sulfonic
acid-2-propylacrylamide, acrylic acid-2-ethyl sulfonate,
methacrylic acid-2-ethyl sulfonate, and butyl acrylamide sulfonic
acid, and salts of them; and monomers each having a phosphonic acid
group such as methacrylic acid-2-ethyl phosphonate and acrylic
acid-2-ethyl phosphonate.
[0050] The chargeable resin pseudo-fine particles to be preferably
used in the present invention are preferably made of a resin having
a glass transition temperature of -40.degree. C. to 60.degree. C. A
glass transition temperature in this range imparts high film
formability to the chargeable resin pseudo-fine particles to cause
colorants adjacent to each other on recording paper to form a film,
so it is capable of forming a strong colored film. Therefore, high
rub-off resistance can be imparted to a printed article obtained by
using the dispersible colorant having such constitution.
[0051] The glass transition temperature of each of chargeable resin
pseudo-fine particles can be measured according to the following
procedure. A dispersible colorant is subjected to acid
precipitation with hydrochloric acid or the like to recover the
precipitate. Furthermore, the precipitate is subjected to Soxhlet
extraction by means of an organic solvent such as tetrahydrofuran
(THF), and then the organic solvent is distilled off to prepare
chargeable resin pseudo-fine particles fixing on a colorant. The
resultant chargeable resin pseudo-fine particle components are
subjected to differential scanning calorimetry to measure the glass
transition temperature. For example, a DSC822e manufactured by
METTLER is desirably used. A water dispersion liquid containing a
dispersible colorant and a water-soluble nonionic resin at the same
time can be separated by means of a centrifugal separator. For
example, when the water dispersion liquid is centrifuged at 12,000
rpm, the dispersible colorant can be obtained as a precipitate.
[0052] Additional functions can be imparted to the dispersible
colorant, and the chargeable resin pseudo-fine particles fixing on
a colorant, of the present invention by appropriately selecting
kinds and copolymerization ratios of monomers each having a radical
polymerizable unsaturated bond of the resin components constituting
the chargeable resin pseudo-fine particles on condition that the
above-described conditions are satisfied. Specific examples of the
monomers include hydrophobic monomers, such anionic hydrophilic
monomers as described above, and nonionic hydrophilic monomers.
[0053] Examples of the hydrophobic monomers include: (meth)
acrylates such as methyl acrylate, ethyl acrylate, isopropyl
acrylate, n-propyl acrylate, n-butyl acrylate, t-butyl acrylate,
benzyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl
methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl
methacrylate, t-butyl methacrylate, tridecyl methacrylate, and
benzyl methacrylate; styrene-based monomers such as styrene,
.alpha.-methyl styrene, o-methyl styrene, m-methyl styrene,
p-methyl styrene, and p-tert-butyl styrene; itaconates such as
benzyl itaconate; maleates such as dimethyl maleate; fumarates such
as dimethyl fumarate; acrylonitrile; methacrylonitrile; and vinyl
acetate.
[0054] Examples of the hydrophilic monomers each having an anionic
group include those described above.
[0055] Specific examples of the nonionic hydrophilic monomers
include: monomers each having a radical polymerizable unsaturated
bond and a hydroxyl group showing strong hydrophilicity in a
structure at the same time such as hydroxyethyl (meth)acrylate and
hydroxypropyl (meth)acrylate; and monomers each containing an
alkylene oxide group such as methoxy polyethylene glycol
(meth)acrylate, ethoxy polyethylene glycol (meth)acrylate,
polyethylene glycol (meth)acrylate, and polypropylene glycol
(meth)acrylate. In addition, various conventionally known or novel
oligomers, macromonomers, and the like can be used without any
limitation.
[0056] The alkylene oxide group-containing monomer is excellent in
copolymerizability with the hydrophobic monomer component, and
provides good results in terms of the uniformity of the surface
properties of the chargeable resin pseudo-fine particles, and
uniform fixing and fusing properties with respect to the
colorant.
[0057] Various properties of the dispersible colorant and the
chargeable resin pseudo-fine particles can be appropriately
controlled by a large number of control factors such as the kinds
and copolymerization ratio of monomers constituting the chargeable
resin pseudo-fine particles and the kind and concentration of a
polymerization initiator to be used at the time of preparation of
the polymer. The chargeable resin pseudo-fine particles are each
particularly desirably composed of a copolymer of monomer
components containing at least one kind of hydrophobic monomer and
at least one kind of hydrophilic monomer out of the monomers listed
above. At this time, the chargeable resin pseudo-fine particles are
each composed by using at least one kind of hydrophobic monomer,
whereby good fixing property with respect to a colorant and good
thermal stability can be imparted. Similarly, the chargeable resin
pseudo-fine particles are each composed by using at least one kind
of hydrophilic monomer, whereby good morphological control and good
dispersion stability can be imparted. Therefore, the simultaneous
use of those monomers provides chargeable resin pseudo-fine
particles which favorably fix on the colorant at all times and have
good dispersion stability.
[0058] Furthermore, in the present invention, a resin obtained from
such monomers as described above by means of a water-soluble
radical polymerization initiator in am aqueous precipitation
polymerization step preferably has a weigh average molecular weight
of 2,000 or more and 20,000 or less. A weight average molecular
weight in this range can remove a resin, which has been polymerized
but is dissolved into a solution without becoming a chargeable
resin pseudo-fine particle, in an ultrafiltration step to be
performed subsequently to the aqueous precipitation polymerization
step, with improved efficiency.
[0059] In the present invention, a chain transfer agent is
preferably used as a molecular weight adjustor to control a
polymerization reaction in order to set the molecular weight in the
above range. Any one of various chain transfer agents can be used
in the present invention. Examples of a particularly effective
chain transfer agent include thiol-based compounds such as lauryl
mercaptan, octyl mercaptan, 2-mercaptoethanol, octyl thioglycolate,
and 3-mercaptopropionic acid. The use of such chain transfer agent
as described above can set the weight average molecular weight of a
resin constituting a dispersible pigment obtained by fixing the
chargeable resin pseudo-fine particles to be 20,000 or less. A
resin having a weight average molecular weight larger than 20,000
has high viscosity when used for ink, so ejection stability which
the present invention aims at achieving is hardly obtained.
[0060] In the present invention, the aqueous precipitation
polymerization step is preferably divided into two stages composed
of: a first stage involving adding one or more kinds of hydrophobic
monomers and one or more kinds of hydrophilic monomers for aqueous
precipitation polymerization by means of a water-soluble radical
polymerization initiator; and a second stage involving further
adding one or more kinds of hydrophilic monomers for aqueous
precipitation polymerization by means of a water-soluble radical
polymerization initiator after the first stage. The reason why such
constitution is preferable is as follows. With such constitution,
the hydrophilicity of a resin not fixing on a colorant can be
enhanced, so the resin not fixing on the colorant can be readily
removed through the ultrafiltration step.
[0061] An example of a particularly suitable combination of
monomers to be used in the present invention includes a combination
of: a hydrophobic monomer containing at least benzyl methacrylate
or a component selected from alkyl (meth)acrylates; and a
hydrophilic monomer containing at least (meth)acrylic acid and a
component selected from methoxy polyethylene glycol
(meth)acrylates, and long-chain alkyl (meth)acrylates each having a
carbon chain having 4 to 40 carbon atoms.
[0062] An example of a suitable combination of monomers to be used
in the present invention when a polymerization reaction is
performed through two stages includes a combination of: a
hydrophobic monomer, to be used in a reaction on a first stage
containing at least benzyl methacrylate or a component selected
from alkyl (meth)acrylates; a hydrophilic monomer to be used in the
reaction on the first stage containing at least (meth)acrylic acid
and a component selected from methoxy polyethylene glycol
(meth)acrylates; and a hydrophilic monomer to be used in a reaction
on a second stage containing (meth)acrylic acid. The amounts of the
respective monomers to be used are preferably as follows. The
hydrophobic monomer to be used in the first reaction on the first
stage contains 95 to 30 parts by mass of benzyl methacrylate with
respect to 100 parts by mass of the entire monomers. The
hydrophilic monomer to be used in the reaction on the first stage
is a mixture containing 1 to 30 parts by mass of (meth)acrylic acid
and 4to 40 parts by mass of one or more components selected from
methoxy polyethylene glycol (meth)acrylates and long-chain alkyl
(meth)acrylates each having a carbon chain having 4 to 40 carbon
atoms with respect to 100 parts by mass of the entire monomers.
[0063] An example of another suitable combination of monomers to be
used in the present invention when a polymerization reaction is
performed through two stages includes a combination of: a
hydrophobic monomer to be used in a reaction on a first stage
containing benzyl methacrylate; a hydrophilic monomer to be used in
the reaction on the first stage containing alkylamine
(meth)acrylate and one or more kinds of components selected from
methoxy polyethylene glycol (meth)acrylates and long-chain alkyl
(meth)acrylates each having a carbon chain having 4 to 40 carbon
atoms; and a hydrophilic monomer to be used in a reaction on a
second stage containing alkylamine (meth)acrylate.
[Synthesis of Chargeable Resin Pseudo-Fine Particle and Fixation
Thereof to Colorant]
[0064] A method of synthesizing the chargeable resin pseudo-fine
particle and a method of allowing the particle to fix on the
colorant can be carried out by the conventional method for the
synthesis of chargeable resin pseudo-fine particles or the
conventional method of making a complex between the chargeable
resin pseudo-fine particles and the colorant whose procedures and
processes are well known in the art. In contrast, the inventors of
the present invention have made extensive studies to invent a
manufacturing method, which is characteristic of the present
invention, with which a dispersible colorant containing a colorant
and a chargeable resin pseudo-fine particle smaller than the
colorant in which the chargeable resin pseudo-fine particle fixes
on the colorant can be easily obtained. Hereinafter, a suitable
method of manufacturing a dispersible colorant with which a
dispersible colorant to be used in the present invention can be
easily obtained will be described.
[0065] The investigation conducted by the inventors of the present
invention has revealed that the dispersible colorant having such
properties as described above can be manufactured very simply by
application of an aqueous precipitation polymerization method under
the conditions below. The manufacturing method involves the steps
of: dispersing a water-insoluble colorant by means of a dispersant
to prepare an aqueous: dispersion liquid of the water-insoluble
colorant; and subjecting a radical polymerizable monomer to aqueous
precipitation polymerization in the aqueous dispersion liquid by
means of an aqueous radical polymerization initiator to allow a
chargeable resin pseudo-fine particle to fix on a colorant. The
dispersible colorant obtained through the aqueous precipitation
polymerization step is a water-insoluble colorant composed of a
colorant on which chargeable resin pseudo-fine particles which have
been synthesized in the aqueous precipitation polymerization step
are strongly fixed in the state of being uniformly dotted. Besides,
the dispersible colorant is excellent in dispersion stability by
itself. In the aqueous precipitation polymerization step, the
properties of the chargeable resin pseudo-fine particle can be
simply adjusted to preferable ones as described above. In this
case, furthermore, the state of fixation of the chargeable resin
pseudo-fine particle on the colorant, which is characteristic of
the present invention, can be attained well. Hereinafter, preferred
embodiments of the above manufacturing method will be described in
more detail.
(Dispersion of Water-Insoluble Colorant)
[0066] First, such water-insoluble colorant to be preferable used
in the present invention as described above is dispersed into a
dispersant to prepare a water dispersing element. Any one of ionic
and nonionic dispersants and the like can be used for dispersing
the colorant into an aqueous solution. Of those, a polymer
dispersant or a water-soluble polymer is desirably used from the
viewpoint of maintaining dispersion stability in a subsequent
polymerization step. One exhibiting sufficient water solubility and
having hydrophobic portions serving as adsorption sites to the
surface of a colorant fine particle and to an oil droplet interface
of a radical polymerizable monomer to be added in a polymerization
step, especially a hydrophobic monomer, is particularly preferably
used. At least one kind of hydrophobic monomer to be used in a
subsequent polymerization step is further desirably present as a
unit constituting a dispersant because the fixation of the
chargeable resin pseudo-fine particles on the colorant in a
subsequent polymerization step can be easily induced.
[0067] Methods of manufacturing a polymer dispersant and a
water-soluble polymer each of which can function as a dispersant
that can be used in the present invention are not particularly
limited. For example, a polymer dispersant or a water-soluble
polymer can be manufactured by allowing a monomer having an ionic
group and another monomer polymerizable with the foregoing monomer
to react with each other in a non-reactive solvent in the presence
or absence of a catalyst. In particular, it has been revealed that
good results can be obtained by using a dispersant selected from
styrene/acrylic polymer compounds each obtained by polymerizing
such monomer having an ionic group as described above and a styrene
monomer as essential ingredients, and ionic group-containing,
acrylic polymer compounds each obtained by polymerizing a monomer
having an ionic group and a (meth)acrylate monomer having 5 or more
carbon atoms as essential ingredients. In the case where a
dispersible colorant to be obtained aims at having, in particular,
an anionic group, an anionic dispersant is desirably selected. On
the other hand, in the case where a dispersible colorant to be
obtained aims at having, in particular, a cationic group, a
dispersant having a cationic group or a nonionic dispersant is
desirably selected.
[0068] An anionic dispersant having an acid value of 100. or more
and 250 or less, or a cationic dispersant having an amine value of
150 or more and 300 or less is desirably used for achieving
compatibility between the promotion of the fixation of the
chargeable resin pseudo-fine particles on the colorant in a
subsequent aqueous polymerization step and the maintenance of the
dispersion stability of the colorant in a polymerization step. When
each of the acid value and the amine value is smaller than the
range, the affinity between the hydrophobic monomer and the
dispersant becomes higher than the affinity between the colorant
and the dispersant at the time of aqueous precipitation
polymerization, so the dispersants is detached from the surface of
the colorant before the chargeable resin pseudo-fine particles fix
on the colorant, and the state of dispersion cannot be maintained
in some cases. When each of the acid value and the amine value is
larger than the range, the excluded volume effect and electrostatic
repulsion of the dispersant on the surface of the colorant become
so strong that the fixation of the chargeable resin pseudo-fine
particles on the colorant is inhibited in some cases. When an
anionic dispersant is used, a dispersant having a carboxyl group as
an anionic group is preferably selected because it does not inhibit
the fixation of the resin fine particles on the colorant.
[0069] In the process of turning the water-insoluble colorant into
the aqueous dispersion liquid by means of the dispersant, the
colorant is dispersed such that the particle size of the dispersed
colorant is preferably 0.1 .mu.m or more and 0.5 .mu.m or less (10
nm or more and 500 nm or less), particularly preferably 0.03 .mu.m
or more and 0.3 .mu.m or less (30 nm or more and 300 nm or less).
The particle size of the dispersed colorant in this process is
greatly reflected in the particle size of the dispersed dispersible
colorant to be obtained. Therefore, the particle size of the
dispersed colorant is preferably within the range from the
viewpoints of the coloring power described above, the
weatherability of an image, and the dispersion stability.
[0070] The particle size distribution of the dispersed
water-insoluble colorant to be used in the present invention is
preferably as monodisperse as possible. In general, the particle
size distribution of the dispersible colorant obtained by the
fixation of the chargeable resin pseudo-fine particles tends to be
narrower than the particle size distribution of the aqueous
dispersion liquid prior to the polymerization step shown in FIG.
2B, but basically depends on the particle size distribution of the
aqueous dispersion liquid described above. In addition, it is
important to narrow the particle size distribution of the colorant
in order to surely induce the fixation of the chargeable resin
pseudo-fine particles on the colorant by virtue of heterogeneous
aggregation. According to the investigation by the inventors of the
present invention, the use of a colorant having a polydispersity
index of 0.25 or less provides a dispersible colorant with
excellent dispersion stability.
[0071] Here, the particle size of the colorant in the state of
being dispersed varies depending on various measurement systems. In
particular, there is an extremely small chance that the organic
pigment is spherical. In the present invention, however, the
average particle size and the polydispersity index used are
obtained by: the measurement, which is performed on the basis of a
dynamic light scattering method with an ELS-8000- manufactured by
Otsuka Electronics Co., Ltd.; and the cumulant analysis of the
results.
[0072] The method of dispersing the water-insoluble colorant into
water may be any one of methods each involving the use of the
dispersant as described above among those by which the colorant can
be stably dispersed into water under such conditions as described
above, and is not specifically limited to any one of the
conventionally known methods. Alternatively, it may be a dispersion
method which is newly developed for the present invention. In
general, for example, when the water-insoluble colorant is a
pigment, a suitable dosage of the polymer dispersant used is
suitably 10 mass % or more and 130 mass % or less with respect to
the pigment.
[0073] The method of dispersing the colorant used in the present
invention is not specifically limited as far as it is any of those
generally used for the respective colorants including: dispersers
such as a paint shaker, a sand mill, an agitator mill, and a
three-roll mill; high-pressure homogenizers such as a
microfluidizer, a nanomizer, and a multimizer; and an ultrasonic
disperser.
(Aqueous Precipitation Polymerization)
[0074] Next, a preferred embodiment of aqueous precipitation
polymerization, which is the process involving synthesizing a
chargeable resin pseudo-fine particle, which is characteristic of
the present invention, and then fixing the chargeable resin
pseudo-fine particle on a colorant. It should be, noted that the
present invention is not limited to any embodiment described below
at all. FIGS. 2A to 2D are process views schematically illustrating
the process flow of the manufacturing method described above. In
this process, the steps to obtain the dispersible colorant can be
thought of as follows. At first, as shown in FIG. 2A, a colorant 1
is dispersed into an aqueous solution by means of a dispersant 3 to
prepare an aqueous dispersion liquid. In this case, the colorant is
adsorbed to the dispersant and thus stabilized in dispersion.
Therefore, the adsorption is in a thermally balanced state. Next,
the aqueous dispersion liquid, which has been prepared in FIG. 2A,
is heated while being stirred, and is added with monomer components
4 together with, for example, an aqueous radical polymerization
initiator 5 (see FIG. 2B). The added aqueous radical polymerization
initiator is heated up, thereby being cleaved to generate radicals
which contribute to a reaction between a hydrophobic monomer
dissolved in a small amount into an aqueous phase and a
water-soluble monomer in the aqueous phase out of the monomer
components added to the aqueous dispersion liquid.
[0075] FIG. 3 is a schematic view that illustrates the steps from
the polymerization of the monomers 4 to the generation of a
dispersible colorant. When the reaction of the monomers 4 described
above proceeds, an oligomer 7 generated by a polymerization
reaction of the monomer components becomes insoluble in water and
is then precipitated from the aqueous phase as a precipitate 8.
However, the oligomer 7 precipitated at this time does not have
sufficient dispersion stability, so it may be combined with other
oligomers to form a chargeable resin pseudo-fine particle 2. The
chargeable resin pseudo-fine particles 2 undergo heterogeneous
aggregation using the hydrophobic surface of the colorant in the
aqueous dispersion liquid as a nucleus, resulting in strong
adsorption caused by the hydrophobic interaction between the
surface of the colorant 1 and the resin component constituting the
chargeable resin pseudo-fine particle 2. At this time, inside the
chargeable resin pseudo-fine particle 2, the polymerization
reaction continues to proceed. Therefore, the particle changes its
form to be more stable with respect to energy while increasing the
number of adsorption points with the colorant 1. Simultaneously,
the inside of the chargeable resin pseudo-fine particle 2 is
highly, physically cross-linked, so the particle can be adsorbed to
the colorant 1 in the most stable manner, thereby resulting in a
fixing state. On the other hand, the colorant 1 becomes stable as
multiple chargeable resin pseudo-fine particles 2 are fixed on the
colorant 1 one after the other. Thus, the dispersant 3 which has
been in the balanced state, is detached from the surface of the
colorant 1 (see. FIGS. 2C and 2D). In the present invention, not
only the dispersant 3 which is detached at this time but also a
resin which has undergone aqueous precipitation polymerization but
is dissolved into a solution without becoming a chargeable resin
pseudo-fine particle can be efficiently removed.
[0076] FIG. 4 shows a schematic view viewed from the interface on
which the chargeable resin pseudo-fine particles 2 thus obtained
fix on the colorant 1. As shown in FIG. 4, in the chargeable resin
pseudo-fine particle, which is an aggregate of resin components,
there are hydrophilic monomer units 9-1, hydrophobic monomer units
9-2, and so one, which are arbitrarily distributed. Therefore,
there are distributed local surface energies and an infinite number
of adsorption points 10 that correspond to the surface energies of
the colorant.
[0077] FIG. 5 shows an enlarged schematic view of the fixing
interface between part of the chargeable resin pseudo-fine
particles 11 and a part 1a of the colorant particle. The interface
of the chargeable resin pseudo-fine particle 11 is adsorbed to the
adsorption point 10 shown in FIG. 4, while being configured so as
to be fit to the surface configuration of the part 1a of the
colorant, thereby resulting in stable fixation. As described above,
in this process, the polymerization reaction still proceeds inside
the chargeable resin pseudo-fine particle. Therefore, the
chargeable resin pseudo-fine particle is adsorbed while keeping the
adsorption in stable, so the fixation thereof on the colorant can
be attained. From the process as described above, the dispersible
colorant constructed as described above can be easily formed (see
FIG. 2D). At this time, in a system where the chargeable resin
pseudo-fine particle has sufficient surface charge and attains its
self-dispersibility, electrostatic repulsion acts between the
chargeable resin pseudo-fine particles, mutually, during the steps
of adsorption and fixation on the colorant with the heterogeneous
aggregation. Therefore, the chargeable resin pseudo-fine particles
are dotted and fixed on the colorant, thereby becoming a preferred
configuration as described above.
[0078] The polymerization reaction conditions may vary depending on
the natures of the polymerization inhibitor, dispersant, and
monomer to be used. For instance, the reaction temperature is set
to 100.degree. C. or lower, preferably in the range of 40.degree.
C. to 80.degree. C. (both inclusive). In addition, the reaction
time period is one hour or more, preferably in the range of 6 hours
to 30 hours (both inclusive). The agitating speed during the
reaction is in the range of 50 rpm to 500 rpm (both inclusive),
preferably in the range of 150rpm to 400 rpm (both inclusive).
[0079] In the step described above, particularly, when a chargeable
resin pseudo-fine particle is obtained by polymerizing a monomer
component containing at least one kind of hydrophobic monomer and
at least one kind of hydrophilic monomer, the monomer component is
desirably added to the aqueous dispersion liquid of the
water-insoluble colorant that contains the aqueous radical
polymerization initiator in advance. Alternatively, the monomer
component is also desirably added dropwise to the aqueous
dispersion liquid of the water-insoluble colorant simultaneously
with, or separately from, the aqueous radical polymerization
initiator. For uniformly obtaining desired chargeable resin
pseudo-fine particles from a mixture of monomers having different
properties, such as the hydrophobic and hydrophilic monomers, it is
favorable to retain the copolymerization ratio of the monomers
having different properties at constant. When an excess amount of
the monomer mixture is added to the polymerization system in
comparison with the amount of monomers to be consumed for a
polymerization reaction in a given time period, there is a tendency
that only specific monomer species are polymerized in advance and
the remaining monomers polymerize after the consumption of the
monomers previously polymerized. In this case, large nonuniformity
occurs in the properties of chargeable resin pseudo-fine particles
to be produced. Of the chargeable resin pseudo-fine particles thus
produced, particularly, those having large contents of hydrophilic
monomer components may not fix on the surface of a colorant.
[0080] Furthermore, a resin component containing hydrophilic
monomer components in large quantities cannot be precipitated in
some cases because of its high hydrophilicity, and the resin
component may remain as a water-soluble resin component in the
system without forming any chargeable resin pseudo-fine particle.
On the other hand, the monomer component is added dropwise to the
aqueous dispersion liquid of the water-insoluble colorant
containing an aqueous radical polymerization initiator, so the
copolymerization ratio between the hydrophobic monomer and the
hydrophilic monomer can be always kept at constant. Therefore, the
chargeable resin pseudo-fine particles constructed with the desired
copolymerization ratio can be obtained uniformly.
[0081] In particular, when an anionic monomer such as acrylic acid
or methacrylic acid is added as a hydrophilic monomer to a
polymerization system, the monomer may be partly destabilized
depending on the properties of a polymer dispersant for dispersing
a colorant to thereby aggregate. For preventing such aggregation,
there is also a preferable embodiments in which the anionic monomer
may be neutralized in advance and added in the state of a sodium
salt or potassium salt.
[0082] Through the above steps, a dispersible colorant in which
chargeable resin pseudo-fine particles each composed of a desired
copolymer fix on the surface of a colorant can be obtained by
controlling a large number of control factors. In particular, when
an anionic monomer is used for the purpose of obtaining high
dispersion stability, the dispersible colorant that has passed the
steps of the present invention can have a large surface functional
group density even when the amount of the anionic monomer to be
used in the above step is relative small, so high dispersion
stability can be imparted. As a result, the dispersion stability of
the chargeable resin pseudo-fine particles can be increased without
any damage to long-term storage stability.
[0083] Although the reason for the above is unclear, the inventors
of the present invention consider as follows. When a radical
generated in water initiates polymerization so that oligomers are
precipitated to form chargeable resin pseudo-fine particles, a
portion having a large amount of components, derived from an
anionic monomer preferentially orients toward an aqueous phase,
that is, the vicinity of the surfaces of the chargeable resin
pseudo-fine particles. This state is maintained even after the
chargeable resin pseudo-fine particles have fixed on a colorant.
Furthermore, in the dispersible colorant to be used in the present
invention having a structurally large specific surface area, a
large number of anionic groups derived from an anionic monomer
component are present. As a result, the dispersible colorant
obtained by means of the manufacturing method described above is
expected to stabilize with the aid of a reduced amount of anionic
monomer components.
[0084] Furthermore, as described above, in order to realize good
ejection stability when the dispersible colorant to be obtained in
the present invention is used as a colorant of ink-jet ink, the
weight average molecular weight of a resin to be obtained through
the above-described aqueous precipitation polymerization step is
preferably adjusted to be 2,000 or more and 20,000 or less. A resin
having a weight average molecular weight larger than the range is
apt to have high viscosity when used for ink. To obtain such
dispersible colorant, a chain transfer agent is preferably used as
a molecular weight adjustor to control the above-described
polymerization reaction. Examples of an available chain transfer
agent include compounds each having a thiol group such as lauryl
mercaptan, octyl mercaptan, 2-mercaptoethanol, octyl thioglycolate,
and 3-mercaptopropionic acid.
[0085] As described above, the method according to the present
invention is characterized in that a colored resin fine particle is
obtained through an ultrafiltration step after aqueous
precipitation polymerization. In the ultrafiltration step, the
dispersant used for dispersing the colorant at the time of the
dispersing step and a resin not forming an emulsion particle can be
removed from the aqueous solution of the dispersing element
containing the dispersible colorant obtained by fixing chargeable
resin pseudo-fine particles. In the present invention, the content
of a resin not fixing on the colorant in 10-mass % aqueous solution
of the dispersible colorant obtained after the ultrafiltration step
is preferably 0.1 mass % or less with respect to the aqueous
solution of the dispersible colorant.
[0086] In the present invention, it is preferable that the pH of an
aqueous solution to be filtered be kept at 9 or more and 13 or
less, and a water-soluble organic solvent be added to carry out
ultrafiltration. When the solution has a pH lower than the range, a
resin not fixing on a colorant in the aqueous solution may
precipitate to clog an ultrafilter. When the solution has a pH
higher than the range, a resin decomposes, so sufficient
dispersibility for dispersing a pigment may not be obtained.
Various organic and inorganic bases can be used to set the pH to be
9to 13. Desirably, bases adaptable to ink-jet ink are used. Of
those, a strong inorganic base such as lithium hydroxide, sodium
hydroxides or potassium hydroxide which has an effect even when it
is added a small amount is most preferable.
[0087] Examples of a preferable water-soluble organic solvent to be
added at the time of the ultrafiltration step include: polyhydric
alcohols such as ethylene glycol, diethylene glycol, triethylene
glycol, polyethylene glycol, polypropylene glycol, propylene
glycol, butylene glycol, 1,2,6-hexane triol, thio glycol, hexylene
glycol, glycerin, trimethylolethane, and trimethylolpropane; alkyl
ethers of polyhydric alcohols such as ethylene glycol monoethyl
ether, ethylene glycol monobutyl ether, diethylene glycol
monomethyl ether, diethylene glycol monoethyl ether, diethylene
glycol monobutyl ether, triethyleneglycol monomethyl ether,
triethylene glycol monoethyl ether, and triethylene glycol
monobutyl ether; 2-pyrrolidone; N-methyl-2-pyrrolidone;
1,3-dimethyl-2-imidizolidinone; and triethanolamine. Any one of
those may be used without any particular limitation. Desirably,
polyhydric alcohols are used in consideration of, for example, the
solubility of a resin not adsorbed to a pigment to be removed. Of
those, diethylene glycol is most desirable in consideration of
general-purpose properties and the like in addition to the
solubility. The amount of the water-soluble organic solvent to be
added is preferably 5 mass % or more and 40 mass % or less with
respect to the aqueous solution containing the dispersible
colorant.
[0088] In the present invention, conditions such as the kind of
membrane to be used for ultrafiltration, a flow rate, and a liquid
path can be appropriately selected in accordance with a substance
to be removed.
[Aqueous Ink]
[0089] The aqueous ink according to the present invention is
characterized by containing the dispersible colorant described
above, and at least one of a water-soluble nonionic resin and an
emulsion particle. When the colorant to be used is a pigment,
typically, the content of the pigment is 0.1 mass % or more and 20
mass % or less, or preferably 0.3 mass % or more and 15 mass % or
less with respect to ink. Furthermore, water or a mixed solvent
containing water and a water-soluble organic solvent as required is
a preferable aqueous medium. Besides, a penetrating agent, an
antiseptic agent, a mildewproofing agent, or the like may be
incorporated to help permeability to the recording medium.
[0090] As shown in FIGS. 1A and 1B, the dispersible colorant to be
used in the present invention is present in the ink in a state
where the chargeable resin pseudo-fine particles 2 fix on the
surface of the colorant 1. Therefore, the colorant adheres to a
recording medium and an adjacent colorant on the recording medium
via the chargeable resin pseudo-fine particles fixing on the
surface. Accordingly, a printed article obtained by, using the
aqueous ink of the present invention has excellent rub-off
resistance.
[0091] Furthermore, when a pigment is used as the colorant, a ratio
of chargeable resin pseudo-fine particles to a pigment (represented
by resin mass/pigment mass=B/P) is desirably set in the range of
0.3 to 4.0 (both inclusive) in the present invention for enhancing
the rub-off resistance of a printed article to be formed by means
of the colorant. Setting the B/P ratio equal to or larger than 0.3
enhances adhesiveness between colorants and adhesiveness between a
colorant and a recording medium, to thereby provide a printed
article with excellent rub-off resistance. In particular, film
formability of aqueous ink using a dispersible colorant obtained by
allowing able resin pseudo-fine particles composed of copolymer
components each having a glass transition temperature of
-40.degree. C. or higher and 60.degree. C. or lower to fix on a
colorant can be expressed with improved effectiveness, whereby
rub-off resistance in glossy paper can be enhanced. When the B/P
ratio is much larger than 4.0 the ink entirely has high viscosity,
and ejection stability may be impaired when the ink is used for an
ink-jet recording apparatus. In-addition, the coloring property of
the colorant on a recording medium is inhibited and a sufficient
printing density is not obtained in some cases because the resin
amount is extremely large as compared to the colorant. Setting the
value of the B/P ratio in the range of 0.3 to 4.0 (both inclusive)
provides aqueous ink that has achieved compatibility between
excellent rub-off resistance and ejection stability in an ink-jet
recording apparatus.
[0092] The term "resin mass" as used herein refers to the total
amount of the chargeable resin pseudo-fine particles in the ink
according to the present invention, and the total amount also
includes the amount of resin components apparently and strongly
adsorbed to a pigment surface in some cases; provided, however,
that the total amount does not include the amount of water-soluble
resin components that can be easily separated from a pigment.
[0093] The value of the B/P ratio described above, which can
generally be determined by means of differential thermogravimetric
analysis, is measured and calculated by means of a TGA/SDTA851
manufactured by METTLER. That is, in the present invention, the
dispersible colorant according to the present invention or aqueous
ink for ink-jet recording containing the dispersible colorant was
centrifuged at 80,000 rpm for 2 hours. The precipitate was dried
and weighed and its temperature was increased in a nitrogen
atmosphere or in the air. A change in mass before and after the
decomposition temperature of each of the pigment and the resin
components at the time of temperature increase was determined to
calculate the B/P ratio.
[Recorded Image]
[0094] The ink according to the present invention can be suitably
used for recording using an ink-jet recording apparatus to be
described later. A recording medium to be used at this time is not
limited, and may be, for example, a medium that enables ink-jet
recording.
[Image Recording Method and Recording Apparatus]
[0095] The dispersible colorant and the aqueous ink containing the
colorant to be used in the present invention can be used in an
ink-jet ejection type head and can be useful for an ink tank in
which such ink is stored or filling ink for the ink tank. In,
particular, out of the different types of ink-jet recording heads,
the present invention exerts excellent effects in bubble jet-type
recording head and recording apparatus.
[0096] As the typical arrangement and principle of the ink-jet
recording system, those practiced by use of the basic principle
disclosed in, for example, U.S. Pat. Nos. 4,723,129 and 4,740,796
is preferable. The above system is applicable to either one of
so-called on-demand type and continuous type. Particularly, in the
case of the on-demand type, the system is effective because, by
applying at least one driving signal, which corresponds to
recording information and gives a rapid temperature rise exceeding
nucleate boiling, to each of electrothermal transducers arranged in
correspondence with a sheet or liquid channels holding ink, heat
energy is generated by the electrothermal transducer to effect film
boiling on the heat acting surface of the recording head, and
consequently, a bubble can be formed in the ink in one-to-one
correspondence with the driving signal. By ejecting the ink through
an ejection opening through the growth and shrinkage of the bubble,
at least one droplet is formed. The driving signal is more
preferably applied as a pulse signal because the growth and
shrinkage of the bubble can be attained instantly and adequately to
achieve ejection of the ink with the particularly high response
characteristics. As the pulse driving signal, signals disclosed in
U.S. Pat. Nos. 4,463,359 and 4,345,262 are suitable. Note further
that excellent recording can be performed by using the conditions
described in U.S. Pat. No. 4,313,124 of the invention, which
relates to the temperature rise rate of the heat acting
surface.
[0097] As an arrangement of the recording head, in addition to the
arrangement as a combination of ejection ports, liquid paths, and
electrothermal transducers (linear liquid paths or right angle
liquid paths) as disclosed in the above specifications, the
arrangement using U.S. Pat. Nos. 4,558,333 and 4,459,600, each of
which discloses the arrangement having a heat acting portion
arranged in a flexed region, is also effective in the present
invention. In addition, the present invention is effectively
applicable to the structure. (e.g., JP 59-123670 A) in which a
common ejection port is used as the ejection portion for multiple
electrothermal transducers. Furthermore, a so-called full-line type
recording head having a length corresponding to the width of the
largest recording medium that can be subjected to recording by the
recording apparatus may be configured by combining multiple
recording heads as disclosed in the above specifications to fill
the length or may be configured as an integrally formed single
head. In each case, the present invention can more effectively
exert the above effects.
[0098] In addition, the present invention is applicable to the use
in an exchangeable chip type recording head which can be
electrically connected to the apparatus main unit and can receive
ink from the apparatus main unit upon being mounted on the
apparatus main unit, and a cartridge type recording head which is
integrally arranged on the recording head itself. It is preferable
to add recovery means, preliminary auxiliary means, or the like,
which is provided as an arrangement of the recording apparatus to
which the present invention is applicable, to the recording head
since the effects of the present invention can be further
stabilized. Specific examples of such means include, for the head,
capping means, cleaning means, pressurization or suction means,
preliminary heating means using electrothermal transducers, another
heating element, or a combination thereof, and means for
preliminary ejection for ejection separate from recording.
EXAMPLES
[0099] Next, the present invention will be further described
specifically with reference to examples and comparative examples.
The present invention is not limited by the following examples
without departing from the gist of the present invention. Unless
otherwise indicated, "part(s)" or "%" in the text is on a mass
basis.
Example 1
[0100] A recording ink 1 to be used for Example 1 was prepared as
follows.
[0101] A mixed solution of 10 parts of carbon black, 6 parts of
glycerin, 10 parts of a styrene/acrylic acid-based resin
dispersant, and 74 parts of water was dispersed at 1,500 rpm for 5
hours using a sand mill manufactured by KANEDA SCIENTIFIC CO., LTD,
thereby obtaining a pigment dispersion liquid 1. In the sand mill,
zirconia beads of 0.6 mm in diameter were used and the filling rate
in a pot was 70%. Black Pearls 880 available from Cabot Corporation
in the U.S. was used as carbon black. The styrene/acrylic resin
used as the dispersant was one having a copolymerization ratio of
70:30, Mw=8,000, and an acid value of 170. The styrene/acrylic
resin was previously added with water and potassium hydroxide
having the above acid value and then the whole was stirred at
80.degree. C. to be turned into an aqueous solution to be used.
[0102] 100 parts of the pigment dispersion liquid 1 thus obtained
were heated to 70.degree. C. in a nitrogen atmosphere. Then, three
solutions each containing a monomer, a chain transfer agent, or a
water-soluble radical polymerization initiator were gradually added
dropwise to the liquid while the liquid was stirred with a motor,
to thereby carry out polymerization. The solutions consisted of (1)
a solution containing 5.7 parts of methyl methacrylate and 1.0 part
of octyl mercaptan, (2) a solution containing 0.3 part, of acrylic
acid, 0.25 part of potassium hydroxide, and 20 parts of water, (3)
a solution containing 0.04 part of potassium persulfate and 20
parts of waters. After the polymerization for 5 hours, the
resultant dispersion liquid was diluted with water by 3-fold, and
the solution was centrifuged at 5,000 rpm for 10 minutes to remove
an aggregated component.
[0103] After that, diethylene glycol and pure water were added to
dilute the resultant by 10-fold in such a manner that the
concentration of diethylene glycol would be 40%. Then, the pH of
the resultant was adjusted to 13 by means of potassium hydroxide.
The resultant solution was purified 8 times in total by means of a
Filtron, centramate ultrafiltration system manufactured by Pall.
The resultant was additionally diluted with pure water by 10-fold,
and then the diluted solution was purified twice in total by means
of the above ultrafiltration system. After that, the resultant was
concentrated to manufacture a dispersible colorant 1. Each
purification was performed under the following conditions. That is,
a pump output and the pressure in a liquid path were adjusted in
such a manner that a total flow rate would be 1 liter/min and a
membrane pressure would be 0.05 MPa.
[0104] The resultant dispersible colorant 1 was dispersed into
water, and the resultant was centrifuged at 12,000 rpm for 60
minutes to re-disperse the precipitate into water. The resultant
was dried, and was observed by means of a scanning electron
microscope JSM-6700 (manufactured by JEOL) at a magnification of
50,000. As a result, a state was observed, in which a chargeable
resin pseudo-fine particle smaller than carbon black as the
colorant fixed to the surface of carbon black. The shape of a
subsequent dispersible colorant described in examples was observed
in the same manner as that described above.
[0105] The content of a resin not fixing on a colorant in an
aqueous solution of a dispersible colorant was measured&by
means of the following method. An aqueous solution was prepared in
such a manner that the concentration of the solid content of the
resultant dispersible colorant 1 would be 10%. Then, the solution
was centrifuged at 25,500 rpm for 3 hours to collect a supernatant
aqueous solution. After the supernatant aqueous solution had been
dried at 120.degree. C. for 2 hours, the remaining solid content
amount was measured. The content of the resin not fixing on the
colorant in the aqueous solution of the dispersible colorant was
determined to be 0.05% from the remaining solid content amount and
the total solid content amount.
[0106] Furthermore the weight average molecular weight of the resin
was measured by means of a Separations Module manufactured by
Waters. The weight average molecular weight Mw was 5,000 in terms
of polystyrene.
[0107] Next, the following components were mixed in such a manner
that the concentration of the above dispersible colorant 1 would be
4%. The mixture was filtered through a membrane filter having a
pore size of 2.5 micron under pressure to prepare an ink 1 of this
example. The total amount of the ink was adjusted with water to be
100 parts. TABLE-US-00001 Glycerin 7 parts Diethylene glycol 5
parts Trimethylolpropane 7 parts Acetylenol EH 0.1 part
Ion-exchanged water Balance
[0108] [Evaluation]
[0109] Recording was performed on CANON PPC paper by means of the
ink 1 thus obtained to evaluate the ink as follows. A BJS 700 was
used as an ink-jet recording apparatus to perform recording. A
specific Bk text was continuously printed on 100 sheets, and the
wetting of a face surface of a head, kogation on a heater board,
and ejection stability after the printing were evaluated by means
of the following method according to the following criteria. Table.
1 shows the results.
(Wetting of Face-Surface)
[0110] The wetting of a face surface was observed with an optical
microscope. The case where no ink droplet was observed around an
ejection port was evaluated as .smallcircle.. The case where an ink
droplet was observed around the ejection port was evaluated as
.DELTA.. The case where a belt-shaped ink droplet was observed
around the ejection port was evaluated as .times..
(Kogation on Heater Board)
[0111] Kogation on a heater board was observed with an optical
microscope after ink in ahead had been completely replaced with
pure water. The case where no kogation was observed on the heater
board was evaluated as .smallcircle.. The case where kogation was
observed on part of the heater board was evaluated as .DELTA.. The
case where kogation was observed on the entire heater board was
evaluated as .times..
(Ejection Stability)
[0112] A specific Bk text was continuously printed on 100 sheets,
and the initial printed article and the last printed article were
compared to evaluate ejection stability according to the following
criteria.
[0113] A: The last printed article has neither stripe nor
unevenness, and the initial and last printed articles are
identical.
[0114] B: The last printed article has a slight stripe, slight
unevenness, or slight slippage, but printing can be performed on up
to 100 sheets without a significant problem.
[0115] C: The last printed article has quality significantly
reduced as compared to that of the initial printed article, or
printing cannot be performed on up to 100 sheets.
Example 2
[0116] 100 parts of the pigment dispersion liquid 1 used in Example
1 were heated to 70.degree. C. in a nitrogen atmosphere. Then,
solutions each containing a monomer, a chain transfer agent, or a
water-soluble radical polymerization initiator were gradually added
dropwise to the liquid while the liquid was stirred with a motor,
to thereby carry out polymerization. The solutions used consisted
of (1) a solution containing 4.28 parts of benzyl methacrylate,
1.42. parts of methoxy polyethylene glycol methacrylate, and 0.1
part of octyl mercaptan, (2) a solution containing 0.3 part of
methacrylic acid, 0.2 part of potassium hydroxide, and 20 parts of
water, (3) a solution containing 0.04 part of potassium persulfate
and 20 parts of water. After the polymerization for 5 hours, the
resultant aqueous solution of a dispersible colorant was diluted
with water by 3-fold, and the solution was centrifuged at 5000 rpm
for 10 minutes to remove an aggregated component.
[0117] After that, diethylene glycol and pure water were added to
dilute the resultant by 10-fold in such a manner that the
concentration of diethylene glycol would be 5%. Then, the pH of the
resultant was adjusted to 9 by means of potassium hydroxide. The
resultant solution was purified 8 times in total by means of a
Filtron, centramate ultrafiltration system manufactured by Pall.
The resultant was additionally diluted with pure water by 10-fold,
and then the diluted solution was purified twice in total by means
of the above ultrafiltration system. After that, the resultant was
concentrated to manufacture a dispersible colorant 2 having a
chargeable resin pseudo-fine particle smaller than a colorant and
fixing on the surface of the colorant. Each purification was
performed under the following conditions. That is, a pump output
and the pressure in a liquid path were adjusted in such a manner
that a total flow rate would be 1 liter/min and a membrane pressure
would be 0.05 MPa.
[0118] The content of a resin not fixing on a colorant in a 10%
aqueous solution of the dispersible colorant 2 and the weight
average molecular weight Mw of the resin were each measured in the
same manner as in Example 1. The content and the weight average
molecular weight were 0.08% and 16,000, respectively.
[0119] Furthermore, an ink 2 was prepared in the same manner as in
Example 1 except that the dispersible colorant 2 was used instead
of the dispersible colorant 1. Furthermore, the resultant ink 2 was
used to form an image in the same manner as in Example 1, and the
image was evaluated in the same manner as in Example 1. Table 1
shows the results.
Example 3
[0120] 100 parts of the pigment dispersion liquid 1 used in Example
1 were heated to 70.degree. C. in a nitrogen atmosphere. Then, the
synthesis of a resin was carried out through two stages consisting
of a first stage and a second stage while the liquid was stirred
with a motor. A reaction on the first stage involved the use of
three kinds of solutions consisting of (1) a solution containing
4.28 parts of benzyl methacrylate, 1.42 parts of methoxy
polyethylene glycol methacrylate, and 0.1 part of octyl mercaptan,
(2) a solution containing 0.3 part of methacrylic acid, 0.2 part of
potassium hydroxide, and 20 parts of water, (3) a solution
containing 0.04 part of potassium persulfate and 20 parts of water.
The mixture containing the dispersion liquid and the three kinds of
solutions was stirred at 70.degree. C. for 5 hours to complete
polymerization on the first stage. Then, a reaction on the second
stage was carried out. The reaction on the second stage involved
the use of a solution containing 0.6 part of methacrylic acid, 0.2
part of potassium hydroxide, and 20 parts of water. The mixture
containing a product as a result of the first stage and the
solution was stirred at 70.degree. C. for 5 hours to carry out a
polymerization reaction. The resultant aqueous solution of a
dispersible colorant was diluted with water. By 10- fold, and the
solution was centrifuged at 5,000 rpm for 10 minutes to remove an
aggregated component.
[0121] After that, diethylene glycol and pure water were added to
dilute the resultant by 10-fold in such a manner that the
concentration of diethylene glycol would be 20%. Then, the pH of
the resultant was adjusted to 13 by means of potassium hydroxide.
The resultant solution was purified 8 times in total by means of a
Filtron, centramate ultrafiltration system manufactured by Pall.
The resultant was additionally diluted with pure water by 10-fold,
and then the diluted solution was purified twice in total by means
of the above ultrafiltration system. After that, the resultant was
concentrated to manufacture a dispersible colorant 3 having a
chargeable resin pseudo-fine particle smaller than a colorant and
fixing on the surface of the colorant. Each purification was
performed under the following conditions. That is, a pump output
and the pressure in a liquid path were adjusted in such a manner
that a total flow rate would be 1 liter/min and a membrane pressure
would be 0.05 MPa.
[0122] The content of a resin not fixing on a colorant in a 10%
aqueous solution of the dispersible colorant 3 and the weight
average molecular weight Mw of the resin were each measured in the
same manner as in Example 1. The content and the weight average
molecular weight were 0.04% and 16,000, respectively.
[0123] Furthermore, an ink 3 was prepared in the same manner as in
Example 1 except that the dispersible colorant 3 was used instead
of the dispersible colorant 1. Furthermore, the resultant ink 3 was
used to form an image in the same manner as in Example 1, and the
image was evaluated in the same manner as in Example 1. Table 1
shows the results.
Example 4
[0124] A dispersible colorant was manufactured in the same manner
as in Example 1 except that three kinds of solutions to be used for
aqueous precipitation polymerization were changed to (1) a solution
containing 4.28 parts of benzyl methacrylate, 1.42 parts of
methoxypolyethylene glycol methacrylate, and 0.1 part of octyl
mercaptan, (2) a solution containing 0.3 part of methacrylic acid
0.2 part of potassium hydroxide, and 20 parts of water, (3) a
solution containing 0.04 part of potassium persulfate and 20 parts
of water.
[0125] After that, diethylene glycol was not used, pure water was
added to dilute the resultant by 10-fold. Then, the pH of the
resultant was adjusted to 12 by means of potassium hydroxide. The
resultant solution was purified 8 times in total by means of a
Filtron, centramate ultrafiltration system manufactured by Pall.
The resultant was additionally diluted with pure water by 10-fold,
and then the diluted solution was purified twice in total by means
of the above ultrafiltration system. After that, the resultant was
concentrated to manufacture a dispersible colorant 4 having a
chargeable resin pseudo-fine particle smaller than a colorant and
fixing on the surface of the colorant. Each purification was
performed under the following conditions. That is, a pump output
and the pressure in a liquid path were adjusted in such a manner
that a total flow rate would be 1 liter/min and a membrane pressure
would be 0.05 MPa.
[0126] The content of a resin not fixing on a colorant in a 10%
aqueous solution of the dispersible colorant 4 and the weight
average molecular weight Mw of the resin were each measured in the
same manner as in Example 1. The content and the weight average
molecular weight were 0.15% and 15,000, respectively.
[0127] Furthermore, an ink 4 was prepared in the same manner as in
Example 1 except that the dispersible colorant 4 was used instead
of the dispersible colorant 1. Furthermore, the resultant ink 4 was
used to form an image in the same manner as in Example 1, and the
image was evaluated in the same manner as in Example 1. Table 1
shows the results.
Example 5
[0128] A dispersible colorant was manufactured in the same manner
as in Example 2 except that octyl mercaptan to serve as a chain
transfer agent was not used.
[0129] After that, diethylene glycol and pure water were added to
dilute the resultant by 10-fold in such a manner that the
concentration of diethylene glycol would be 20%. Then, the pH of
the resultant was adjusted to 13 by means of potassium hydroxide.
The resultant solution was purified 8 times in total by means of a
Filtron, centramate ultrafiltration system manufactured by Pall.
The resultant was additionally diluted with pure water by 10-fold,
and then the diluted solution was purified twice in total by means
of the above ultrafiltration system. After that, the resultant was
concentrated to manufacture a dispersible colorant 5 having a
chargeable resin pseudo-fine particle smaller than a colorant and
fixing on the surface of the colorant. Each purification was
performed under the following conditions. That is, a pump output
and the pressure in a liquid path were adjusted in such a manner
that a total flow rate would be 1 liter/min and a membrane pressure
would be 0.05 MPa.
[0130] The content of a resin not fixing on a colorant in a 10%
aqueous solution of the dispersible colorant 5 and the weight
average molecular weight Mw of the resin were each measured in the
same manner as in Example 1. The content and the weight average
molecular weight were 0.20% and 100,000, respectively.
[0131] Furthermore, an ink 5 was prepared in the same manner as in
Example 1 except that the dispersible colorant 5 was used instead
of the dispersible colorant 1. Furthermore, the resultant ink 5 was
used to form an image in the same manner as in Example 1, and the
image was evaluated in the same manner as in Example 1. Table 1
shows the results.
Comparative Example 1
[0132] A dispersible colorant 6 was manufactured in the same manner
as in Example 1 except that: the amount of octyl mercaptan used was
changed to 0.1 part; and no ultrafiltration was performed.
[0133] The content of a resin not fixing on a colorant in a 10%
aqueous solution of the dispersible colorant 6 and the weight
average molecular weight Mw of the resin were each measured in the
same manner as in Example 1. The content and the weight average
molecular weight were 4.0% and 15,000, respectively.
[0134] Furthermore, an ink 6 was prepared in the same manner as in
Example 1 except that the dispersible colorant 6 was used instead
of the dispersible colorant 1. Furthermore, the resultant, ink 6
was used to form an image in the same manner as in Example 1, and
the image was evaluated in the same manner as in Example 1. Table 1
shows the results. TABLE-US-00002 TABLE 1 Evaluation results
Comparative Example Example Ink 1 Ink 2 Ink 3 Ink 4 Ink 5 Ink 6
Wetting of .smallcircle. .smallcircle. .smallcircle. .DELTA.
.DELTA. x face surface Kogation on .smallcircle. .smallcircle.
.smallcircle. .DELTA. .DELTA. x heater board Ejection A A A B B C
stability
[0135] This application claims priority from Japanese Patent
Application No. 2004-190472 filed on Jun. 28, 2004, which is hereby
incorporated by reference herein.
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